Quantitative estimates of the potential effectiveness of backfill barriers based on a linear sorption node! are presented. Using getters such as clays (known sorbent3), a backfill approximately l-foot-thick can delay 4 5 \ 3 by 10 to 10 years the breakthrough of transuranics. A delay of 10 years is possible for major cationic fission products. These delays can be achieved provided that (1) the distribution coefficient (K , a measure of affinity for sot bed species) for the barrier maternal is equal to or greater than 2000 ml/g for transuranics and 200 ml/g for fission products; (2) the interstitial groundwater velocity through the barrier is limited to J ft/year or less; (3) the effective porosity of the barrier is equal to or less than 0.1; and (4) the physical integrity of the barrier is maintained (no channels or cracks!. Mixtures containing expanding clays such as smectites and other getters, are expected to 3atisfy these criteria.

Brine flow has been measured to unheated boreholes for periods of a few days and to heated holes for two years in the WIPP facility. It is proposed that Darcy flow may dominate the observed influx of brine. Exact solutions to a linearized model for one-dimensional, radial flow are evaluated for conditions approximating the field experiments. Flow rates of the correct order of magnitude are calculated for permeabilities in the range 10−21–1020 m2 (1–10 nanodarcy) for both the unheated and heated cases.

This paper describes preliminary interpretation of in-situ pressure and flow measurements of the Salado Formation at the Waste Isolation Pilot Plant (WIPP). The WIPP facility is located 660 m underground in the Salado, a bedded salt deposit. Shut-in pressure tests were conducted prior to, and subsequent to, the mining of a circular drift in order to evaluate excavation effects on pore pressure, permeability, and host rock heterogeneity. Borehole deformation was measured during these tests and used to correct for changes in the test region volume due to salt creep effects. Preliminary pre-excavation results indicate that the flow properties of this layered host rock are heterogeneous. Resulting pore pressures range from 1 to 14 MPa and permeabilities range from below measurable to about 1 nanodarcy. Normalized borehole diameter change rates were between -4 and 63 microstrains/day. Shut-in pressures and borehole diameters in all test boreholes were affected by the excavation of Room Q coincident with the advances of the boring machine. Preliminary results from post-excavation test results show decreased pore pressures compared to pre-excavation values.

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